Image transfer

ABSTRACT

Apparatus for electrostatically transferring images formed by photoelectrophoresis. The color balance of the images which are made up of electrically photosensitive particles on a transparent conductive substrate are modified during electrostatic transfer by exposure to electromagnetic radiation to which at least a portion of the particles are sensitive.

United States Patent 1 Carreira et a].

[541 IMAGE TRANSFER [75] Inventors: Leonard M. Carreira, Webstemlra S.Stein; Vsevolod Tulagin, both of 4 Rochester, all of N.Y. [73] Assignee:Xerox Corporation, Rochester, NY. 22 Filed: Dec. 4, 1969 [21] Appl.No.:879,962

Related US. Application Data [62] Division of Ser. No. 542,050, April12, 1966, Pat.

[52] Cl. ..355/16, 96/l.2, 355/4 [51] Int. Cl. ..-.G03g 15/00 [58] Fieldof Search ....355/l6, 3, 4; 96/1, 1.2, 1.3, 96/l.4

[451" Jan. 16,1973

[56] References Cited UNITED STATES PATENTS 2,968,552 l/l96l Gundlach..3s5/3x Primary ExarninerSamuel S. Matthews Assistant Exar'ninerRichard L. Moses AttorneyStanley Z. Cole, James J. Ralabate andRonald Zibelli I [5 7] ABSTRACT Apparatus for electrostaticallytransferring images formed by photoelectrophoresi's. The color balanceof the images which are made up of electrically photosensitive particleson a transparent conductive substrate are modified during electrostatictransfer by exposure to electromagnetic radiation to which at least aportion of the particles are sensitive.

12 Claims, 4 Drawing Figures PATENTEDJAH 16 I975 3 71 l 196 SHEET 1 [IF2 IMAGE TRANSFER CROSS REFERENCE TO RELATED APPLICATIONS BACKGROUND OFTHE INVENTION This invention relates in general to imaging systems andmore specifically to a photoelectrophoretic imaging system.

In photoelectrophoretic imaging, the imaging particles which aregenerally intensely colored are suspended in an insulating carrierliquid. This suspension is then placed between a pair of electrodes,subjected to a potential difference and exposed to an image to bereproduced. Ordinarily, when carrying out the process, the imagingsuspension is placed on a transparent electrically conductive plate inthe form of a thin film and exposure is made through the bottom of thisplate while a second electrode is brought into contact with the top ofthe suspension, while a potential is applied across the twoelectrodes.The particles are believed to bear an initial charge when suspended inthe liquid which causes them to be attracted to the transparent baseelectrode and to change polarity by exchanging charge with this baseelectrode upon exposure so that the exposed particles migrate across tothe upper electrode to form an image on the base electrode by particlesubtraction. This image is clearly and easily visible on the baseelectrode after the upper electrode carrying the particles which are notused to form part of the image is separated from the base electrode. Thesystem may be used to produce monochromatic images by using a singlecolor of particles in the suspension or a number of differently coloredparticles in the suspension which respond to the light exposure. Inpolychromatic systems, mixtures of two or more differently coloredparticles which are each sensitive only to light of a specific differentwavelength or narrow range of wavelengths are used. Thus, for example, afull color image may be produced by using a mixture of cyan,

magenta and yellow particles which respond to red,

green and blue light respectivelysAn extensive and.

detailed description of a photoelectrophoretic imaging technique of thetype described above is found in copending application Ser. No. 384,737,now US. Pat. No. 3,384,565 filed July 23, 1964, which is incorporatedherein by reference.

Although the electrophoretic imaging technique generally described abovehas been found to be capable of producing excellent quality images inboth monochromatic and polychromatic systems, it is frequentlyundesirable to leave the final image on the transparent base electrode.Thus, for example, when a very high quality optically flat reusableelectrode is employed, the use of a new electrode each time the imagingprocess is carried out might, make the process prohibitively expensivefor Another problem is that the electrode may not have any physicalproperties most desired as the final imaging substrate so that if theimage is made on a conductive transparent glass substrate, it must betransferred to some other surface if a flexible print is to be produced.Although transfer of the image may be accertain applications.

complished by bringing an adhesive into contact with it and stripping itaway, such adhesive materials are relatively expensive and frequentlydifficult and messy to work with. In addition to the aforementionedproblems it has also been found that there is sometimes left behind onthe electrode some unwanted imaging particles that tend to form a dirtybackground on the final image, and in other instances where apolychromatic color system is involved the color balance of the image asformed on the electrode needs corrections because one or more of theparticles in the system responds to the imaging steps either more orless vigorously than it should to form a perfect color image of theoriginal.

SUMMARY OF THE INVENTION Further objects will become apparent to thoseskilled in the art'as the disclosure is more fully made.

I The above and still further objects may be accomplished in accordancewith the present invention by transfer of the image after it has beenformed on one of the imaging electrodes by bringing a transfer substrateinto close proximity with the formed image and applying an electricalfield across the image in such a direction as to transfer it (i.e., theimage) to the transfer substrate. Any suitable technique may be employedfor applying the electrical field including, for example, bringing aroller, plate or other conductive elements connected to a high potentialsource closely adjacent to the back of the transfer substrate orapplying a high potential corona discharge to the back of the transfersubstrate while bringing it into proximity with the image. Since it isbelieved that the particles, remaining after the imaging electrode haspassed over the imaging suspension, have a non-uniform chargedistribution, that is, some are positively charged and some arenegatively charged, the polarity of the applied field can be eitherpositive or negative. In its preferred form however, the polarity of theapplied field will be opposite to the polarity applied to the imagingelectrode;

thus, if the imaging electrode is negatively charged, the

transfer electrode is positively charged, and vice versa. This is sobecause it is believed that the majority of the particles constitutingthe particle image are charged the same as the charge on the imagingelectrode. Such ing the transfer step to improve, alter or otherwisemodify transfer. Ithas been found, forexample, that 1 transfer from thebase electrode onto the transfer substrate is more efficient whenexposure of the image to the original being reproduced is continuedduring the transfer step. Transfer can also be effectedwhen the image isilluminated uniformly with white light during the transfer step. Inanother modification of the. process, filtered light of selectedwavelengths may be used to expose the image during transfer for colorcorrection or partial image transfer of polychromatic images usingimaging particles of two or more colors.

BRIEF DESCRIPTION OF THE DRAWINGS glass 12 overcoated with a thinoptically transparent layer 13 of tin oxide. Tin oxide coated glass iscommer cially available under the tradename NESA glass from thePittsburgh Plate Glass Company of Pittsburgh, Pennsylvania. This baseelectrode 'will be referred to hereinafter as the injecting electrode.Coated on the upper surface of electrode 11 is a thin layer 14 of finelydivided photosensitive particles dispersed in an insulatthe formedparticle image and applying an electric field ing carrier liquid. Thissuspension may also contain binders for the particles whichare dissolvedor suspended along with the particles in the carrier liquid. Adjacentelectrode 11 is a roller electrode generally designated 16 mounted forrotation on a rigid plate 18. The electrode 16 is connected in thisinstance to the negative side of a potential source 20 with the oppositeside of the source being connected .to ground. Since the tin oxide layerof injecting electrode 11 is also connected to ground, an electric fieldis applied across the liquid suspension when electrode 16 rolls acrossthe surface of electrode 11 in the direction indicated by the arrow 22inthe drawing. Electrode 16 is made up of a central core 24 which ispreferably of fairly high electrical con- .ductivity and this core iscovered with a layer of a blocking electrode material 26, which may, forexample, consist of Baryta paper (a paper coated with a gelatinsuspension of barium sulphate). An image projector made up of a lightsource 28, atransparency 30, and a lens 32 is provided to exposesuspension 14 to a light image of the original transparency 30 'to bereproduced. This electrode surface 26 collects unwanted (i.e. exposed)particles from suspension 14 as it rolls across electrode 11 duringexposure,as explained in copending application Ser. No.'384,737, now US.Pat. No. 3,384,565 and leaves a particle image corresponding to thetransparency to be reproduced on reused. It has been found that theparticle image can be efficiently transferred to a more desirablesurface by across the image in such a direction so as to transfer it tothe transfer substrate.

Referring back to FIG. 1,- there is seen a third electrode generallydesignated 34 which is, in this instance, also mounted for rotation onrigid plate 18. This electrode 34 will be referred to hereinafter as thetransfer electrode. Transfer electrode 34 is, in this embodiment,similar in constructionto electrode 16; that is, electrode 34 is made upof a conductive core 36 covered with a transfer surface 38, such asBaryta paper sleeve,

regular bond paper or onion skin paper. Conductive core 36 is connectedby any suitable means to a potential source 40. The potential applied toconductive core 36 is, in this embodiment, of opposite polarity to thepotential applied to electrode 16;

Accordingly, electrode 34 is connected to the positive side of potentialsource 40 with the opposite side of the source being connected toground. Since the tin oxide layer 13 on injecting electrode 11 is alsocon-' nected to ground, an electric field is applied across liquidsuspension 14 when electrode 34 rolls across the surface of electrode'11 in the direction indicated by arrow 22in the Figure. In this manner,the particle image is cleanly transferred to transfer electrode 34. Iftransfer electrode 34 is covered with a: removable transfer surface,such as Baryta paper sleeve, for'example, as previously disclosed, thecomplete image is transferred to surface 38, which can then be removedand replaced with a new sleeve for use in subsequent transfers. Afterelectrodes 16 and 34 have traveled across liquid suspension 14 in thedirectionindicated by arrow 22, they are raised slightly and returned totheir initial position along the path indicated by arrow 42. Y

F IG. 2 shows an alternate embodimentof' the structure of transferelectrode 34. In this 1 embodiment, transfer electrode 34 is made up'ofa continuous web 44 of a conductive material having a'suitable transfersurface 45. Web 44 carried, by plate 18 in the form of by any suitablemeans, such as by a set of conductive rollers 50."The electric fieldapplied to the back of web' 44 is, once again, of opposite polarity tothat of 'elec{ trode 16 so that the particles left behind during thepassage of electrode 16 are attracted to web 44.

FIG. 3 shows'an alternate embodiment of the manner in which the field isapplied across the imaging suspension. In this Figure,like numerals havebeen used to identifyparts of the apparatus which are identical to 2.The embodiment shown here in FIG. 3 is the same as the FIG. 2 embodimentexcept for the'distinctions hereinafter noted, including the fact thatthe potential is applied to the back of transfer web 44 by means of highpotential corona discharge device 52. Such a' device is more fullydescribed in 1 US. Pat. No. 2,588,699. Rollers 54'are used to keep thetransfer web surface under tension sufficient to maintain the transfersurface in a flat condition, whereby its entire applicable surface isplaced in direct contact with liquidsuspension 14 during the transferstep. Each potential source 20 and 40 is individuallygrounded ratherthan having their opposite poles connected and then grounded as in FIG.2 Here, as distinguished from FIGS. 1 and 2, the polarity of thepotential applied to electrode 34 is the same as the polarity of thepotential applied to electrode 16. As has previously been set forth,since it is believed that the particles, remaining after the imagingelectrode has passed over the imaging suspension, have a nonuniformcharge distribution, that is, some are positively charged and some arenegatively charged, the polarity of the applied field can be eitherpositive or negative. In this particular embodiment an imaging apparatusisshown wherein the polarity of the field applied to the transferelectrode is negative (i.e., the same polarity as is applied to theimaging electrode).

FIG. 4 represents a side sectional view of an embodiment of theinvention after imaging electrode 16 has rolled over the exposedphotosensitive suspension. In this instance, imaging electrode 16 is ofthe tractor type having aconductive inner web 56 covered with a layer ofblocking electrode material 58, such as Baryta paper. Electrode 16 isconnected to the negative side of a potential source 20 by means ofroller contacts 60 and plate contact 62. The roller contacts alsoperform the auxiliary function of holding surface 58 under tensionsufficient to maintain that surface in a flat condition, therebyenabling the entire applicable surface to be placed in direct contactwith exposed suspension 14 as electrode 16 rolls thereover during theimaging operation. In this embodiment of the invention, electrode 16 hasbeen caused to roll across the top surface of injecting electrode 11during the period of image exposure. This light exposure causes theexposed particles originally attracted to electrode 11 to migratethroughthe suspension and adhere to surface 58 of electrode 16, leavingbehind a particle image 14' on the injecting electrode surface which isa duplicate of original-transparency 30. Passage of transfer electrode34 over injecting electrode 11 during application of an electric fieldacross the image 14 will cause the image to adhere to transfer surface44, thereby resulting in a duplicate of original transparency ontransfer surface 44.

Asexplained in Ser. No. 384,737, now U.S. Pat. No. 3,384,565 the systemcan produce monochromatic or polychromatic images depending upon thetype and number of particles suspended in the liquid carrier and thecolor of light to which the suspension is exposed in the'process.

In addition to transferring image 14 from the surface of injectingelectrode 1 l to transfer surface 38 or 44 by applying an electric fieldacross the particle image, it has now been found, quite unexpectedly,that exposure to actinic electromagnetic radiation during the transferoperation enhances the transfer of the final image. In one aspect ofthis illumination, exposure through transparency 30 is continued duringthe passage of electrode 34 over the surface of injecting electrode.This imagewise exposure has been found to result in a more efficienttransfer of particle image 14 than when transfer is accomplished in theabsence of additional actinic electromagnetic radiation.

In another aspect, it has been found that transfer may be aided byflooding particle image 14' uniformly with white light during transfer.This can be accomplished by rotating original transparency 30 aroundpivot 64 (see FIG. 4) so that it is out of the path of the white lightemanating from source 28.

It is also contemplated that transfer can be effected by electrode 34while image 14 is subject to actinic electromagnetic radiation having asingle wavelength or a selected band of wavelengths, which can beaccomplished by any suitable means, for example, by rotatingtransparency 30 about pivot 64 out of the path of illumination fromlight source 28 and moving filter 66, also pivoted about point 64 forconvenience into said illumination path. In the event that more than onetype of photosensitive particle is used in the imaging suspension, eachtype being responsive to a different (or overlapping) portion of thevisible spectrum, it has been found that an excellent transfer occurswhen the particle image is flooded uniformly with actinicelectromagnetic radiation having a wavelength (or a selected band ofwavelengths) at which the particles in suspension 14 are equallyresponsive or as nearly equally responsive as nature permits. Forexample, where the suspension comprises a dispersion of phthalocyanine,Algol Yellow, andWatchung Red in a liquid carrier, (as described in Ser.No. 384,737 now U.S. Pat. No. 3,384,565), effective transfer occurs whenthe particle image is flooded with blue light of approximately 400 m.p..wavelength. Thus, it has been found that a relatively low intensitylight of correct wavelength is far more effective than white light(whose absolute intensity made the orders of magnitude greater, yetproduces less than complete transfer). It is also contemplated thattransfer can be effected by electrode 34 while image 14' is subjected toactinic electromagnetic radiation which is passed through bothtransparency 30 and filter 66, thereby resulting in imagewiseillumination of a particular wavelength (or a selected band ofwavelengths only).

With respect to the production of color images (that is, wheresuspension 14 contains two or more photosensitive particles which areresponsive to different wavelengths in the visible portion of thespectrum) it has been found that proper illumination, as hereinafterdescribed, during transfer will aid in color correction of the finalimage (i.e., the image transferred to electrode 34), should a colorimbalance exist in the image 14' as it is viewed on electrode 11 priorto transfer. For purposes of illustration, this aspect of the inventionwill be described with reference to a suspension having threephotosensitive particles; namely,

- cyan, yellow and magenta therein.

After image 14' is formed by the passage of electrode 16 over thesurface of injecting electrode 11, the image may look to be off color(i.e., imbalanced) because of an unexpected photoresponse in one or moreof the particles in suspension 14. For example, if the image is viewedin white light and it appears to be too red, this is because the cyanparticles responded too readily to the original exposure so that thereare not enough cyan I particles left behind in image 14' to filter outthe proper amount of red light from the white light source. To remedythis color imbalance, it will be necessary to transfer magenta andyellow particles to the transfer electrode 34 at a relatively lower ratethan cyan particles are transferred. It has been found that this colorcorrection can be achieved by illuminating image 14 with a light sourcewhich is deficient in the color (or 7 colors) cotresponding to theparticle (particles) which an analgous manner, if the image appears tobetoo blue when viewed in white light, transfer is conducted while theimage is subjected to illumination from a light source which isdeficient in blue light (e.g., by passing white light through a yellowfilter) and if the image appears to be too green, then transfer isconducted'while the image is illuminated with a light source which isdeficient in green light (e.g., by passing white light through a magentafilter). Passage of electrode 34 over image 14' during suchillumination, while under a potential of opposite polarity to thepotential applied to the imaging electrode, will result in the transferof an image, in proper color balance, to the surface of the transferelectrode. Y

C onvers' e'ly, an imbalanced color image can be color corrected byselectively transferring, at a relatively greater rate, the remainingphotosensitive particles corsystem are reversed, electrode 11 willpreferably be capable of accepting injected holes from bound particlesupon exposure tolight and electrode 16 would preferably be a blockingelectrode incapable of injecting holes into the particles at more than avery slow rate when they come into contact with the surface of this 7electrode. In this preferred embodiment, electrode ll may be composednot only of conventional conductive materials such as'tin oxide, copper,copper iodide, gold or the like, but may also include manysemiconductive materials such as raw'cellophane which are notordina'rily thought of asconductors, but which are. stilltcapable ofaccepting injected charge carriers of thebecause charge which leaves theparticles initially responding to the particle (or particles) which has(have) exhibited the unexpected photoresponse. It has been found thatthis can be achieved by illuminating image 14' with a light source whichis richer in light corresponding to the particle which has exhibitedtheunexpected photoresponse. I

1 For example, if the particle mixprevi'ously disclosed is,"once again,too re'd, this selective transfer with the resultant color correction ofthe final image can be achieved by exposing image 14 during transfer toillumination which, is rich in red light (e.g., by passing a thetransfer of an image, in proper color balance, to the surface of the-transfer electrode. In this manner, more cyan particleswill betransferred (in a relative nature) than yellow particles or magentaparticles and, in so do-,

bound on this surface upon exposure to light can merely move out of theparticles and remain on the insulating surface therebyallowing theexposed particles to migrate. However, the use of the more conductivematerials is preferred because it allows for cleaner charge separationin that charge leaving the particles upon exposure can move into theunderlying surface and away from the particle in which it originated.This also prevents'possible charge build-up on the electrode which mighttend to diminish the inter-electrode field;

Onthe other hand, the preferredembodiment of the blocking electrode 16isselectedso as to prevent or greatly retard the injection of electrons(or holes, depending upon the initial polarity of charge on theparticle) into a bound particle when it reaches the surface of thiselectrode. Accordingly, the surface of this electrode facing suspension14 in the preferredembodiment may be either an insulator or asemiconductor I which will not allow for the passage of sufficientcharge mg, image '14 will be brought back into color balance. 7

ln an analogous manner, if the imageappearsto be too 7 ,blue orgreen'when viewed in white light transfer is conducted while the imageis subjected to illumination from alight source which is rich in blue orgreen light the transfer electrode-as it'passes over image 14, is

I under'a potential of the'same polarity .as the potentiaoriginallyappliedto the imaging electrode.

As 'should be clear at this pointin the disclosure,

respectively. This corrective exposure is made while there are certainpreferred properties for e lectrode's l 1.

carriers under the influence of the applied field to discharge theparticles finally bound to it, thereby preventingparticle oscillationIinthe system. Even if this blocking electrode will allow for the passageof some charge carriers through it to the particles, will still beconsidered to come within the class of preferred materials if it doesnot allow for the passage of sufficient carriers to recharge theparticles to the opposite polarity because even a discharge particlewill tend to adhere to this blocking electrode by Van Der Waals forces.Here again materials not coming within the preferred class may beemployed but they tend to lead to particle oscillation in the system,resulting in lower image density, poor image-resolution, image reversaland similar deficiencies, with the degree of these de ficiencies, inmost instances, depending upon h owfarthe material employed deviatesfrom the preferred class of I i 1 materials infits electricalcharacteristics.

suspension 14 when it (i.e., the particle) is exposed to.

blocking electrode which is incapable of injecting elec' trons into sucha bound particle at more than a very.

slow rate when it comes into contact with the surface of the electrode16. Obviously, if all polarities in the Baryta paper and other suitable"materials may be I employed to surface the blockingelectrode and maybewet on their'back surfaces with electrically conductive materials.

Although this invention has been-described for the most-part inconnection with a- Baryta paper covered imaging electrode 116 andtransfer electrode 34, any

suitable material having aresistivity of about l0 ohm cm. or greater maybe. employed, as a preferred. material- Typical materials inthisr'esistivity range -inwill not adversely affect the transfer of theparticle image to the transfer electrode.

Applicable carrier liquids and photosensitive imaging particles, and thepreparation and composition of the imaging suspension have already beendescribed in Ser. No. 384,737, now US. Pat. No. 3,384,565 and thatcopending application should be referred to for such additionaldisclosure. A more detailed listing of applicable photosensitiveparticles can be found in copending application, Ser. No. 518,041, nowUS. Pat. No. 3,383,993 filed Jan. 3,- 1966, which list is incorporatedherein by reference. This latter list is of greatest interest wherecolor originals are being reproduced and, of course, is ofparticular'interest with respect to the manner in which a suspension ofa plurality of different photosensitive particles is color corrected foran imbalance in image 14 as heretofore set forth.

It should be understood that the heretofore described processes areapplicable to a repetitive or cyclic process, that is, where all or someof the following steps are performed, completely removing the imagingsuspension from its supporting electrode after imaging and transfer(e.g., by cleaning the electrode of residual particles that may remainafter transfer), applying a new imaging suspension to the electrode, and

repeating the imaging and transfer operations at least one additionaltime.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The followingexamples are givento enable those skilled in the art to more clearly understand andpractice the invention. They should not be considered as a limitationupon the scope of the invention,-but merely as being illustrativethereof.

EXAMPLES roughly 3 inches square and is exposed as described in eachparticular example.

EXAMPLEl A suspension including 1.5 grams of Watchung Red B, a bariumsalt of 1-(4'-methyl-5-chloro-azobenzene- 2-sulfonic acid)-2-hydroxy-3-naphthoic a'cid, C.l. No. 15865, available from DuPont; 2grams Algol Yellow o.c.,l,2,5,6-di(C,C-diphenyl)-thiazole-anthraquinone, C.l. No. 67300,available from General Dyestuffs; and 1.5 grams Monolite Fast Blue G.S.,the alpha form of metal-free phthalocyanine, C.l. No. 74100, availablefrom Arnold Hoffman Co.; is made up in 50 milliliters of Sohio OdorlessSolvent 3440 (a kerosene fraction available from Standard Oil Company ofOhio). These particles are magenta, yellow, and cyan respectively. Thismixture, known as tri-mix, is coated on a NESA glass substrate andexposed with a light intensity of 1,800 foot candles. A Kodachrome colortransparency is placed between the light source and the NESA glasssubstrate so that a colored image is projected onto this tri-mix as theimaging electrode moves across the surface of the glass. The imagingelectrode has a polyvinylidene fluoride covering thereon and the rolleris held at a negative potential of 2,500 volts with respect to the glasssubstrate. After the imaging electrode passes over the substrate, anexcellent quality subtractive threecolor image corresponding to theKodachrome transparency is left behind on the glass. A Baryta papercovered transfer electrode which is employed is held at a positivepotential of 2,500 volts with respect to the glass substrate. After thetransfer electrode passes over the remaining particle image left behindon the glass, a

good quality image is obtained on the surface of the Baryta paper.

EXAMPLE ll The procedure of Example I is repeated including exposure ofthe particle image during transfer to uniform white light from the 1,800foot candle light source. A

fair quality image is obtained on the Baryta paper transfer surface.

EXAMPLE III quality image is now obtained on the Baryta paper transfersurface.

EXAMPLE IV The procedure of Example I is repeated except that the Barytapaper covered transfer electrode is held at a negative potential of2,500 volts with respect to the glass substrate. The poor quality imageis obtained on the transfer surface.

EXAMPLE V The procedure of Example IV is repeated including exposure ofthe particle image during transfer to uniform white light from the 1,800foot candle light source. A good quality image is obtained on thetransfer surface.

EXAMPLE VI 3,000 volts, and the transfer electrode is held at a posi-.

tive potential of 3,000 volts. After the imaging elec-' trode passesover the substrate, an excellent quality three-color image is leftbehind on the NESA glass, and after the transfer electrode passes overthe particle image, a good quality image is obtained on the Baryta papertransfer surface.

EXAMPLE vu The procedureof Example V1 is followed with the further stepof exposing the particle image during transfer to uniform white lightfrom the800 foot candle light source. A good quality image is obtainedon the Baryta paper transfer surface.

EXAMPLE V111 The procedure of Example V1 is followed with the additionaloperation of exposing the particle image during transfer 'to light whichhas passed through the original Kodachrome color transparency. Asuperior quality image is obtained on the surface of the Baryta papertransfer paper.

EXAMPLE IX The procedure of Example V1 is followed except thatapproximately 2 mol percent 2,4,7-trinitro-9- fluorenone sensitizer isadded to the tri-mix suspension.

A good quality image is obtained on the NESA glass substrate when alight source of 250 foot candles is vused. A good quality image is alsoobtained on the Baryta paper transfer surface when the particle image isexposed to the 250 foot candle light source during transfer.

EXAMPLE X A suspension including equal amountsof Watchung Red B, AlgolYellow GC and Monolite Fast Blue GS is 7 made up in Sohio solvent withtotal particle concentrationapproximately percent by weight. Thismixture is coated on a NESA glass substrate and exposed with a lightintensity'of 1,800 foot candles. A Kodachrome color transparency ispassed between the light source thereon and is held at a negativepotential of 2,500

volts with respect to the glass substrate. After the imaging electrodepasses over the substrate, a good quality subtractive three-color imagecorresponding to the Kodachrome transparency is produced on the glass;however, the image when viewed in white light appears too green. ABaryta paper covering transfer electrode which is employed is held atapositive potential of 2,500 volts with respect to the glass substrate.During the passage of the transfer electrode over the colorv EXAMPLEXI Asuspension including 1.0 grams of Watchung Red B, 1.5 grams of theyellow particle of Example V and 1.25 grams Monolite Fast Blue 0.8. ismade up in 50 milliliters Sohio Odorless Solvent 3440. Theprocedure ofExample X is followed except that the Baryta paper covering transferelectrode is held at a negative potential of 2,500 volts with respecttothe glass substrate. After theimaging electrode passes over thesubstrate, a

good quality subtractive three-color image corresponding to theKodachrome transparency, except that the image when viewed in whitelight appears to be too red, is left behind on the glass. During thepassage of the transfer electrode over the remaining particle image leftbehind on the glass substrate, the image is exposed to visible lightwhich is more intense in the red portion of the visible spectrum than inother portions. This is achieved by passing the white light from the1,800 foot candle source through a Wratton red filter. A good qualitycolor corrected image is obtained on the surface of the transferelectrode.

EXAMPLE Xll The procedure of Example V1 is followed with the furtherstep of exposing the particle image during transfer to blue light ofapproximately, 400 m.p.. wavelength. This exposure is achieved bypassing white light from the 800 foot candle source through a Wra't tenblue filter. A superior quality image is obtained on the Baryta papertransfer surface. v

While the invention has been described ,with reference to preferredembodiments thereof, it will be understood by ,those skilled in the artthat various changes in form and details may be made without departingfrom the true spiritand scope of the invention.

It should be understood that the present invention is not dependent uponthe exact nature of the photose nsitive particles employed, rather anysuitable particle composition (either in pure form or admixed withother. photosensitive or non-photosensitive materials) or structure maybe employed,provided the advantageous results of this invention are notadversely affected.

Further, as will be apparent to those skilled in-the art, additionaloperations may be performed to achieve the herein disclosed results or,in certain circumstances, certain operations may be deleted. Theapparatus herein disclosed may be modified in numerous ways to, onceagain, achieve the effective transfer heretofore set forth. All suchadditions, deletions, modifications, etc. are considered to be withinthe scope of the present invention.-

What is claimed is:

l. A photoelectrophoretic imaging apparatus comprising a smoothoptically transparent first electrode for supporting a layer of animaging suspension comprising electrically photosensitive particles inan insulating carrier liquid, a second electrode for uniformlycontacting the free surface of an imaging suspension on said firstelectrode, means for applying a potential difference between said firstand said second electrodes, means for exposing a suspension on saidfirst electrode through said first electrode to radiation to which atleast a portion of the particles in the imaging suspension areresponsive until an image is formed on said first electrode, a transfermember for contacting an image on said first electrode, means forapplying a potential difference between said transfer member and saidfirst electrode, means for exposing an image on said first electrode toonly a portion of the wavelengths in the visible light spectrum whilesaid transfer member is in contact with the image.

2. The apparatus of claim 1 wherein said transfer member is in the formof-a roller.

3. The apparatus of claim 1 wherein said transfer member is in the formof a continuous web.

4. The apparatus of claim 1 wherein said transfer member comprises aconductive support having an insulated covering thereon.

5. The apparatus of claim 1 wherein said transfer member comprises aconductive support having a semiconductive covering thereon.

6. The apparatus of claim 1 wherein said means for applying a potentialdifference between'said transfer member and said first electrode is acorona discharge unit.

7. A photoelectrophoretic imaging apparatus com prising a smoothoptically transparent first electrode for supporting a layer of animaging suspension comprising electrically photosensitive particles inan insulating carrier liquid, a second electrode for uniformlycontacting the free surface of an imaging suspension on said firstelectrode, means for applying a potential difference between said firstand said second electrodes, means for exposing a suspension on saidfirst electrode through said first electrode to radiation to which atleast a portion of the particles in the imaging suspension areresponsive until an image is formed on said first electrode, a transfermember for contacting an image on said first electrode, means forexposing an image on said first electrode to visible light which is lessintense in at least one portion of the visible spectrum while saidtransfer member is in contact with the image.

8. The apparatus of claim 7 wherein said transfer member is in the formof a roller.

9. The apparatus of claim 7 wherein said transfer member is in the formof a continuous web.

10. The apparatus of claim 7 wherein said transfer member comprises aconductive support having an insulated covering thereon.

11. The apparatus of claim 7 wherein said transfer member comprises aconductive support having a semiconductive covering thereon.

12. The apparatus of claim 7 wherein said means for applying a potentialdifference between said transfer member and said first electrode is acorona discharge unit.

2. The apparatus of claim 1 wherein said transfer member is in the formof a roller.
 3. The apparatus of claim 1 wherein said transfer member isin the form of a continuous web.
 4. The apparatus of claim 1 whereinsaid transfer member comprises a conductive support having an insulatedcovering thereon.
 5. The apparatus of claim 1 wherein said transfermember comprises a conductive support having a semi-conductive coveringthereon.
 6. The apparatus of claim 1 wherein said means for applying apotential difference between said transfer member and said firstelectrode is a corona discharge unit.
 7. A photoelectrophoretic imagingapparatus comprising a smooth optically transparent first electrode forsupporting a layer of an imaging suspension comprising electricallyphotosensitive particles in an insulating carrier liquid, a secondelectrode for uniformly contacting the free surface of an imagingsuspension on said first electrode, means for applying a potentialdifference between said first and said second electrodes, means forexposing a suspension on said first electrode through said firstelectrode to radiation to which at least a portion of the particles inthe imaging suspension are responsive until an image is formed on saidfirst electrode, a transfer member for contacting an image on said firstelectrode, means for exposing an image on said first electrode tovisible light which is less intense in at least one portion of thevisible spectrum while said transfer member is in contact with theimage.
 8. The apparatus of claim 7 wherein said transfer member is inthe form of a roller.
 9. The apparatus of claim 7 wherein said transfermember is in the form of a continuous web.
 10. The apparatus of claim 7wherein said transfer member comprises a conductive support having aninsulated covering thereon.
 11. The apparatus of claim 7 wherein saidtransfer member comprises a conductive support having a semi-conductivecovering thereon.
 12. The apparatus of claim 7 wherein said means forapplying a potential difference between said transfer member and saidfirst electrode is a corona discharge unit.